The goal of this project is to determine whether impaired insulin secretory function can be detected preceding the onset of NIDDM in subjects at high risk (women with previous gestational diabetes), and to evaluate whether physiologic subsets of this population can be defined which predict distinct underlying gene defects. Preliminary studies suggest combined use of the Bergman minimal model and measurement of insulin secretion by C-peptide deconvolution improves assessment of the insulin sensitivity-insulin secretion relationship.